The student who brought the gun said, “I’m sorry,” when it went off and ran to another classroom, said Deputy Chief Patrick Gannon of the Los Angeles Police Department. The student, whose name has not been released, was taken into custody and moved to a downtown police station while the school was locked down.

The gun was apparently in a backpack, and it went off when the backpack was dropped, said a spokesman for the L.A. United School District. A 15-year-old girl was hit in the head and was in critical condition and a 15-year-old boy suffered a neck wound and was in serious condition. Authorities said both injuries were probably caused by one bullet.

The episode will likely spotlight screening procedures at schools across the US as well as public and parental responsibility, say criminologists. They worry that public reaction could lead to calls for more metal detectors, video surveillance, and sign-in procedures that, they say, tend to create a fortress mentality for schools – even though incidents of shooting deaths remain extremely rare.

“In the immediate short term, you can understand parents and public desire for increased protections,” says James Alan Fox, a criminologist at Northeastern University and author of “Violence and Security on Campus: from Pre-school through College.” But from 1999 to 2005, he notes, fewer than 100 school-age children were killed in school homicides, compared with 105 in storms, over 1,000 in bicycle accidents, and 800 in pool drownings.

Yet “over several years I heard from school administrators that parents complained so much about school shootings, the schools invested in systems for which they didn’t have enough money and had to cut back on the educational curriculum for which they exist – from teachers to books to after school programs,” says Professor Fox.

Nationally about 10 percent of junior and high schools have metal detectors, Fox says. Gardena High School checks incoming students with security wands at the entrance. It is not yet clear known how comprehensive or random such checks are.

Metal detectors and video systems don’t work because, while trying to make the children feel more protected, they highlight their vulnerability, Fox says. “Sometimes they present a challenge to the kinds of kids who want to prove to their school that they can get around the system,” he adds. “If you want to get a gun into school around a metal detector, you can do it very easily but using a window.”

The Los Angeles Times reports that the student had brought a gun to school "a couple times before," according to a friend. The friend, Andrea Tibbs, said the student had felt threatened after he had been in a fight outside school.

Discipline is reportedly a long-term problem at Gardena High School. Approximately 35 percent of students drop out, the Associated Press reports, and five years ago, 2,000 suspensions were given out and 15 students expelled. By last year, however, those numbers had dropped to 300 and two, respectively.